Performance Analysis And System Optimization Of Dimmable Visible Light Communication

Recently,visible light communication(VLC)has been attracted much attention all over the world.VLC technology is developed based on the existing LED lighting facilities,and we only need to add communication modules on the existing LED lighting fixtures.The realization is convenient and the cost is low.Indoor visible light communication is a integration technology of communication and lighting,So we must take account of user demands of communication and lighting performance.The main contents of this paper include the performance of single-carrier,multi-carrier and multi-color dimming communication in visible light communication.For single-carrier dimming communication mode,We use multi-pulse position modulation(MPPM)to dimming communication,and set up its dimming control model.Quantized noise is used to evaluate the service quality of dimming control.The upper bound of communication rate is replaced by the achievable communication rate based on signal-to-noise ratio.The multi-objective optimization method is used to balance the dimming and communication performance.The selection criteria of system parameters under corresponding dimming level are given.For multi-carrier dimming communication mode,OFDM has been widely used in high speed VLC systems.We propose an enhanced asymmetrically clipped DC-biased optical OFDM(eADO-OFDM)for dimming communication.The main idea is to generate asymmetric OFDM signals by integrating DC-biased optical OFDM(DCO-OFDM)and asymmetrically clipped optical OFDM(ACO-OFDM).The signal power ratio changes with dimming level.It can sufficiently utilize asymmetric LED dynamic range and improve the spectrum efficiency.For this dimming control scheme,We formulate a capacity maximization optimization problem that satisfies corresponding constraints and needs.Numerical results demonstrate that the proposed eADO-OFDM outperforms ACO-OFDM and DCO-OFDM.For multi-color dimming communication mode,White light illumination is required to ensure for multi color LED in VLC systems,so the power distribution of different colors maps to the chromatic figure with a restricted elliptical region,called MacAdam Ellipse.The optimal power allocation changes with dimming level under the demands of dimming and communication.Then we formulate an optimization problem of dimming communication for RGB LEDs in VLC systems,and propose a novel two-step algorithm to solve the optimization problem with lower implementation complexity.